1. Field of the Invention
The present invention is directed to ink jet printheads, and in particular to ink jet printheads having an ink manifold and channel plate, and to methods of making manifolds and channel plates for ink jet printheads. 2. Description of the Related Art
Generally speaking, drop-on-demand ink jet printing systems can be divided into two types. The type using a piezoelectric transducer to produce a pressure pulse that expels a droplet from a nozzle or the type using thermal energy to produce a vapor bubble in an ink-filled channel that expels a droplet. This latter type is referred to as thermal ink jet printing or bubble ink jet printing. In existing thermal ink jet printing, the printhead comprises one or more ink filled channels, such as disclosed in U.S. Pat. No. 4,463,359 to Ayata et al, (the disclosure of which is incorporated herein by reference) communicating with a relatively small ink supply chamber at one end and having an opening at the opposite end, referred to as nozzle. A thermal energy generator, usually a resistor, is located in the channels near the nozzle a predetermined distance therefrom. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble which expels an ink droplet. As the bubble grows, the ink bulges from the nozzle and is contained by the surface tension of the ink as a meniscus. As the bubble begins to collapse, the ink still in the channel between the nozzle and bubble starts to move towards the collapsing bubble, causing a volumetric contraction of the ink at the nozzle and resulting in the separating of the bulging ink as a droplet. The acceleration of the ink out of the nozzle while the bubble is growing provides the momentum and velocity of the droplet in a substantially straight line direction towards a recording medium, such as paper.
In U.S. Pat. No. 4,463,359, a thermal ink jet printer is disclosed having one or more ink-filled channels which are replenished by capillary action. A meniscus is formed at each nozzle to prevent ink from weeping therefrom. A resistor or heater is located in each channel at a predetermined distance from the nozzles. Current pulses representative of data signals are applied to the resistor to momentarily vaporize the ink in contact therewith and form a bubble for each current pulse. Ink droplets are expelled from each nozzle by the growth of the bubbles which causes a quantity of ink to bulge from the nozzle and break off into a droplet at the beginning of the bubble collapse. The current pulses are shaped to prevent the meniscus from breaking up and receding too far into the channels after each droplet is expelled. Various embodiments of linear arrays of thermal ink jet devices are shown such as those having staggered linear arrays attached to the top and bottom of a heat sinking substrate and those having different colored inks for multicolored printing. In one embodiment, a resistor is located in the center of a relatively short channel having nozzles at both end thereof. Another passageway is connected to the open-ended channel and is perpendicular thereto to form a T-shaped structure. Ink is replenished to the open-ended channel from the passageway by capillary action. Thus, when a bubble is formed in the open-ended channel, two different recording mediums may be printed simultaneously.
One preferred technique for fabricating thermal ink jet printheads is disclosed in U.S. Pat. No. Re. 32,572 to Hawkins et al (the disclosure of which is incorporated herein by reference). Each printhead is composed of two parts aligned and bonded together. One part (known as a heater plate) is a substantially flat substrate which contains on the surface thereof a linear array of heating elements and addressing electrodes, and the second part (known as a channel plate) is a substrate having at least one recess anisotropically etched therein to serve as an ink supply reservoir when the two parts are bonded together. A linear array of parallel grooves are formed in the second part, so that one end of the grooves communicate with the reservoir recess and the other ends are open for use as ink droplet expelling nozzles. Many printheads can be made simultaneously by producing a plurality of sets of heating element arrays (heater plates) with their addressing electrodes on a silicon wafer and by placing alignment marks thereon at predetermined locations. A corresponding plurality of sets of channels and associated reservoirs (channel plates) are produced in a second silicon wafer and, in one embodiment, alignment openings are etched thereon at predetermined locations. The two wafers are aligned via the alignment openings and alignment marks, then bonded together and diced into many separate printhead modules. A number of printhead modules can be fixedly mounted in a pagewidth configuration which confronts a moving recording medium for pagewidth printing. Alternatively, individual printhead modules can be used to form carriage type printheads as shown in FIG. 1 of U.S. Pat. No. Re. 32,572.
These printheads are typically mounted on a heat sink so that the heater plate is in physical contact with the heat sink. The individual addressing electrodes are then wire bonded to corresponding electrodes on a printed wire board (see FIGS. 2-4 of U.S. Pat. No. Re. 32,572). An ink manifold is typically sealed to a surface of the channel plate opposite from the surface containing the channels so that ink contained in an ink supply can be supplied to the reservoir in the channel plate through the ink manifold.
These ink manifolds can be made from a hard plastic material by a one step injection molding process.
FIG. 1 is a block diagram of a conventional process for fabricating thermal ink jet printheads such as the printhead shown in FIG. 2. A hard plastic manifold 18 is injection molded (S1) and heater and channel plates 12, 15, respectively are fabricated in silicon wafers (S2, S3). The heater and channel wafers are infrared aligned and an epoxy 13 is used to adhesively bond channel plates 15 of the channel wafer to heater plates 12 of the heater wafer to form a wafer assembly (S4, S5, S6). The wafer assembly is diced into many individual printhead modules 17 by using a dicing blade, the wafer assembly is ultrasonically cleaned, and then individual printhead modules 17 are separated from the diced wafer assembly (S7-S9). For more details on this fabrication process see, for example, U.S. Pat. No. 4,786,357 to Campanelli et al.
After the nozzle-containing front face of each printhead module is coated with a hydrophobic substance, the adhesive bonding each channel plate to each corresponding heater plate is totally cured (S10). Printhead modules 17 can then be used to make either a carriage type or a full-width thermal ink jet printhead. A full-width thermal ink jet printhead is formed as either a butted array or a staggered array of individual printhead modules, while only one diced printhead module is required to form a carriage type printhead (although plural printhead modules can be stacked to improve resolution or provide for multiple colors in carriage-type printheads as disclosed in U.S. Pat. No. 4,833,491 to Rezanka).
As shown in FIG. 2, printhead module 17 (shown with its subparts) is bonded to manifold 18 and heat sink 16 to complete the fabrication of the thermal ink jet printhead. An adhesive 14, such as, for example, silver epoxy, is applied to heat sink 16, and the printhead module 17 is bonded to heat sink 16 by curing adhesive 14 (S11-S13). A printed wire board (PWB) is applied to the heat sink (S14), and is wire-bonded to the addressing electrodes of the heater plate (S15). Finally, manifold 18 is sealed to printhead module 17 by using, for example, an RTV sealant 19, and manifold 18 is then secured to heat sink 16, also with epoxy (S16-S18).
The above fabrication method is disadvantageous because: (1) precise alignment and dicing of the wafer assembly is difficult; (2) the use of adhesive 13 to bond channel plate 15 to heater plate 12 increases the likelihood that the channels will become clogged by the adhesive during fabrication; and (3) the total process is time consuming and cost inefficient due to the numerous fabrication steps, and careful adhesive application process involved.
U.S. Pat. No. 4,866,461, to Piatt discloses a top shooter printhead of a carriage type. A print cartridge comprises a base member having an opening and a heater/electrode access slit. The base member can be formed of molded plastic and can include ink channeling structures extending from the opening to the slit. By virtue of its material composition, the base member provides easy attachment of other components that cooperate to form the print cartridge. An ink supply housing is attached to the base member by bonding or mechanically coupling its opening to the base member. Further, a cover member is bonded to face of the base member opposite from the ink supply housing. The cover member can be formed of molded plastic and have nozzle-defining apertures therein. Alternatively, the cover can be molded as part of the base member, and a separate orifice plate can be attached to the base member opposite to the slit. The heater/electrode can be secured into the slit, for example, by epoxy bonding, with heating elements approximately flush with the inner surface of the base member.
U.S. Pat. No. 4,635,073 to Hanson discloses a top shooter printhead for insertion into a cartridge. A plastic header is made from an injection molding process, and includes a central ink storage region for receiving ink and feeding the ink into an elongated slot of a thin film resistor substrate. The elongated slot serves as an ink intake port for providing ink to a plurality of ink reservoirs and to corresponding ink injection orifices in an orifice plate.
U.S. Pat. No. 4,727,012 to Quella et al. discloses a side shooter printhead of an ink jet printer. An ink jet chamber is manufactured by an injection molding method. The ink channel and the discharge openings, i.e., nozzles, are manufactured by a multilayer structure composed of a plurality of individual photoplastic films.
U.S. Pat. No. 4,330,787 to Sato et al. discloses the construction of a liquid jet recording device. The liquid jet recording device comprises a plurality of grooves formed in a liquid feeding path plate at positions corresponding to each of a plurality of heat generating elements contained on a heater plate; and a plurality of grooves formed in a liquid discharge path plate at positions corresponding to the grooves. The plates for the liquid feeding path and liquid discharge path may be made of glass, ceramics and, depending on the circumstances, various plastics having heat resistant properties. A manifold is also provided for supplying ink to the grooves in the liquid discharge path plate.
U.S. Pat. No. 4,536,777 to Matsumoto discloses a side shooter printhead of a liquid jet recording apparatus. A liquid jet section comprises a base plate of Fotoceram in which an orifice, a liquid path and an air vent are etched; and a stainless steel top plate having an etched opening in which the energy generating element is to be mounted. The base plate, top plate and the energy generating element are assembled into a unit by the use of any suitable adhesive. A box-like member defines a liquid chamber and is closed at its top opening by a closure which may be injection molded from a thermoplastic resin and adhesively bonded to the top opening. The liquid jet section is then assembled into the box-like member to form a recording head.
None of the above U.S. patents discloses a thermal ink jet printhead having an elastomer channel plate, or injection molding a channel plate into a manifold. Further, none of the above U.S. patents discloses a heater plate and a channel plate assembled to each other without the use of adhesive to secure the channel plate to the heater plate.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
U.S. patent application Ser. No. 07/789,490 to Anikara Rangappan filed Nov. 8, 1991 and entitled "A Method of Manufacturing Page Wide Thermal Ink-Jet Heads" discloses full-width channel plates formed by injection molding techniques. The channel plates are molded from ceramic "Green Tape" or a hard plastic molding material such as polysulfone.